Many temperature controlled commercial enclosed spaces need to be equipped with pressure relief ports or vents which are sometimes referred to as ventilators or ventilator ports. This is particularly true where the sealed space is subjected to temperature related gas volume variations that must be relieved.
Many of these enclosed spaces require that a positive air pressure differential to ambience be maintained. However there are spaces where no differential is required or desired. Passive ports are suitable for these enclosures. However existing passive pressure relief ports, meaning those without fans or blowers, have often permitted air migration where there is no significant pressure differential. With walk-in freezers this causes undesirable condensation and frosting. Frosting is a substantial problem that occurs as ambient warm air drawn into a low temperature chamber releases significant amounts of moisture relative to the change in dew point of the air at high and low temperatures. Air is drawn through the port after each door opening cycle as the warm air that entered the enclosure cools and contracts. If venting does not occur, a partial vacuum results which make it difficult to reopen the door. In extreme cases, the enclosures can even collapse.
A temperature rise in the enclosure between cooling cycles, and especially during a defrost cycle, creates a need to vent air to prevent pressure buildup. Again, failure to vent this pressure, with adequate relief capacity, can cause the chamber to rupture.
Passive pressure relief ports are in wide commercial use today. Large structures require the movement of a large amount of air to equalize the pressure between the inside and the outside of the enclosure. Existing vents can be either of a large size or a gang of small sized vents. This large amount of air carries with it a large amount of moisture. This moisture can condense almost immediately upon contact with the cold air and cold surfaces of the enclosure. If this occurs, a large ice block may form on the interior wall, which may eventually block the inflow of air through the port. This large ice block may also pose a potential danger to someone should it fall from the wall.
Accordingly, it is seen that a need exists for a passive pressure relief port, i.e. one that is not electrically powered by fans and baffles, yet which substantially prevents the formation of ice blocks within the enclosure. It thus is to be provision of such a pressure relief port that the present invention is primarily directed